Pneumatic tire

ABSTRACT

In an internal pressure state where an internal pressure that is 0.05 times a normal internal pressure P has been increased to the normal internal pressure P, amounts of protrusions at points Pa, Ph, Pd, and Pe are represented as Da (mm), Dh (mm), Dd (mm), and De (mm), respectively. A sum Fa (((Dd+De)/W)×100) of the amounts of protrusions for each sidewall  6  satisfies mathematical expressions (2) and (3) in which an aspect ratio A is used, and a difference Gs (((Da−Dh)/W)×100) in the amount of protrusion for a tread  4  satisfies mathematical expressions (5) and (6). 
       0.02626× A −1.8615&lt; Fa    (2)
 
         Fa &lt;0.02626× A −0.6615   (3)
 
       −0.010819× A −0.084658&lt; Gs    (5)
 
         Gs &lt;−0.010819× A +0.6713   (6)

TECHNICAL FIELD

The present invention relates to pneumatic tires.

BACKGROUND ART

Various pneumatic tires that include treads having improved wearresistance and various pneumatic tires in which tread surfaces includegrooves having improved crack resistance, have been suggested.

In JP2-106404, a pneumatic tire is suggested in which a tread includesgrooves having improved crack resistance. For this tire, a radius ofcurvature of the tread, and an amount of protrusion of the tread in thecase of the tire being inflated with air are specified. For this tire,it is suggested that a difference between an amount of protrusion at thecenter of the tread and an amount of axially outward protrusion of thetread is set so as to be within a predetermined range. In this tire,change of an amount of protrusion of the tread and change of the radiusof curvature of the tread are reduced when a low internal pressure stateshifts to a standard internal pressure state.

In JP58-112804, a radius of curvature of a tread and a shape ofshoulder-side wall portions are specified. Thus, a pneumatic tire issuggested in which resistance to uneven wear of the tread, and crackresistance in grooves are improved. For this tire, it is suggested thata difference between shapes of the tread and the shoulder portions inthe case of the tire being inflated with air, and shapes of the treadand the shoulder portions in a forming mold, is set so as to be within apredetermined range. For this tire, change between the shape of the moldfor the tire and the shape of the tire inflated with air, is reduced.

CITATION LIST Patent Literature

Patent Literature 1: JP2-106404

Patent Literature 2: JP58-112804

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

Components of a pneumatic tire are elastic members. When the tire isinflated with air, stress is generated to change the shape of the tireto a balanced shape. The change of the shape is unavoidable in pneumatictires. Therefore, the inventers have advanced development of a tire inwhich its shape is changed so as not to reduce wear resistance, andcrack resistance in grooves when the tire is inflated with air.

An object of the present invention is to provide a pneumatic tire thatis excellent in resistance to uneven wear, and crack resistance ingrooves.

Solution to the Problem

A pneumatic tire according to the present invention includes: a treadhaving an outer surface that forms a tread surface; a pair of sidewallsthat extend almost inward from ends, respectively, of the tread in aradial direction; a carcass that is extended along inner sides of thetread and the sidewalls; and a belt that is disposed outward of thecarcass in the radial direction and layered over the carcass. The belthas an inner layer, and an outer layer disposed outward of the innerlayer in the radial direction and layered over the inner layer. Thetread surface has grooves.

A position, on an equator plane, of the tread surface is represented asa point Pa. Positions, on the tread surface, which are distant from eachother by 0.8 times a width Wb, in an axial direction, of a region wherethe inner layer and the outer layer of the belt are layered over eachother, are each represented as a point Ph. Positions, on axially outerside surfaces of the sidewalls, which are distant from each other with amaximum width, are each represented as a point Pe. Positions, on theaxially outer side surfaces of the sidewalls, each of which is amidpoint between the point Pa and the point Pe in the radial direction,are each represented as a point Pd. A nominal width is represented as W(mm).

In an internal pressure state where an internal pressure that is 0.05times a normal internal pressure P has been increased to the normalinternal pressure P, an amount of protrusion at the point Pa isrepresented as an amount of protrusion Da (mm), an amount of protrusionat the point Ph is represented as an amount of protrusion Dh, an amountof protrusion at the point Pd is represented as an amount of protrusionDd (mm), and an amount of protrusion at the point Pe is represented asan amount of protrusion De (mm).

When a sum Fa of the amounts of protrusions for each sidewall isobtained according to mathematical expression (1), the sum Fa of theamounts of protrusions satisfies mathematical expressions (2) and (3) inwhich an aspect ratio A is used, and

when a difference Gs in the amount of protrusion for the tread isobtained according to mathematical expression (4), the difference Gs inthe amount of protrusion satisfies mathematical expressions (5) and (6).

Fa=((Dd+De)/W)×100   (1)

0.02626×A−1.8615<Fa   (2)

Fa<0.02626×A−0.6615   (3)

Gs=((Da−Dh)/W)×100   (4)

−0.010819×A−0.084658<Gs   (5)

Gs<−0.010819×A+0.6713   (6)

Preferably, the tire includes a band disposed outward of the belt in theradial direction and layered over the belt. The band includes a fullband, and a pair of edge bands layered over end portions, in the axialdirection, of the full band. The full band includes a cord and a toppingrubber. The cord extends substantially in the circumferential direction.Each edge band includes a cord and a topping rubber. The cord extendssubstantially in the circumferential direction or the axial direction.

Preferably, in the tire, the aspect ratio A is 70%. The sum Fa of theamounts of protrusions is greater than −0.02 and less than 1.18. Thedifference Gs in the amount of protrusion is greater than −0.84 and lessthan −0.09.

Preferably, in the tire, the aspect ratio A is 40%. The sum Fa of theamounts of protrusions is greater than −0.81 and less than 0.39. Thedifference Gs in the amount of protrusion is greater than −0.52 and lessthan 0.24.

A durability evaluation method for a pneumatic tire according to thepresent invention is a durability evaluation method for a tire whichincludes: a tread having an outer surface that forms a tread surface; apair of sidewalls that extend almost inward from ends, respectively, ofthe tread in a radial direction; a carcass that is extended along innersides of the tread and the sidewalls; and a belt that is disposedoutward of the carcass in the radial direction and layered over thecarcass, and in which: the belt has an inner layer, disposed outward ofthe inner layer in the radial direction and layered over the innerlayer.

In the tire, a position, on an equator plane, of the tread surface isrepresented as a point Pa. Positions, on the tread surface, which aredistant from each other by 0.8 times a width Wb, in an axial direction,of a region where the inner layer and the outer layer of the belt arelayered over each other, are each represented as a point Ph. Positions,on axially outer side surfaces of the sidewalls, which are distant fromeach other with a maximum width, are each represented as a point Pe.Positions, on the axially outer side surfaces of the sidewalls, each ofwhich is a midpoint between the point Pa and the point Pe in the radialdirection, are each represented as a point Pd. A nominal width isrepresented as W (mm).

In a case where, in an internal pressure state where an internalpressure that is 0.05 times a normal internal pressure P has beenincreased to the normal internal pressure P, an amount of protrusion atthe point Pa is represented as an amount of protrusion Da (mm), anamount of protrusion at the point Ph is represented as an amount ofprotrusion Dh, an amount of protrusion at the point Pd is represented asan amount of protrusion Dd (mm), and an amount of protrusion at thepoint Pe is represented as an amount of protrusion De (mm),

wear resistance of the tread and crack resistance in the grooves aredetermined as being good,

when a sum Fa of the amounts of protrusions for each sidewall isobtained according to mathematical expression (1), the sum Fa of theamounts of protrusions satisfies mathematical expressions (2) and (3) inwhich an aspect ratio A is used; and

when a difference Gs in the amount of protrusion for the tread isobtained according to mathematical expression (4), the difference Gs inthe amount of protrusion satisfies mathematical expressions (5) and (6).

Fa=((Dd+De)/W)×100   (1)

0.02626×A−1.8615<Fa   (2)

Fa<0.02626×A−0.6615   (3)

Gs=((Da−Dh)/W)×100   (4)

−0.010819×A−0.084658<Gs   (5)

Gs<−0.010819×A+0.6713   (6)

A manufacturing method for a pneumatic tire according to the presentinvention is a manufacturing method for a tire which includes: a treadhaving an outer surface that forms a tread surface; a pair of sidewallsthat extend almost inward from ends, respectively, of the tread in aradial direction; a carcass that is extended along inner sides of thetread and the sidewalls; and a belt that is disposed outward of thecarcass in the radial direction and layered over the carcass, and inwhich: the belt has an inner layer, disposed outward of the inner layerin the radial direction and layered over the inner layer. Themanufacturing method includes determining and evaluating durability of asample tire.

In the determining and evaluating of durability, a position, on anequator plane, of the tread surface is represented as a point Pa,positions, on the tread surface, which are distant from each other by0.8 times a width Wb, in an axial direction, of a region where the innerlayer and the outer layer of the belt are layered over each other, areeach represented as a point Ph, positions, on axially outer sidesurfaces of the sidewalls, which are distant from each other with amaximum width, are each represented as a point Pe, positions, on theaxially outer side surfaces of the sidewalls, each of which is amidpoint between the point Pa and the point Pe in the radial direction,are each represented as a point Pd, and a nominal width is representedas W (mm).

In a case where, in an internal pressure state where an internalpressure that is 0.05 times a normal internal pressure P has beenincreased to the normal internal pressure P, an amount of protrusion atthe point Pa is represented as an amount of protrusion Da (mm), anamount of protrusion at the point Ph is represented as an amount ofprotrusion Dh, an amount of protrusion at the point Pd is represented asan amount of protrusion Dd (mm), and an amount of protrusion at thepoint Pe is represented as an amount of protrusion De (mm),

it is determined that,

when a sum Fa of the amounts of protrusions for each sidewall isobtained according to mathematical expression (1), the sum Fa of theamounts of protrusions satisfies mathematical expressions (2) and (3) inwhich an aspect ratio A is used; and

when a difference Gs in the amount of protrusion for the tread isobtained according to mathematical expression (4), the difference Gs inthe amount of protrusion satisfies mathematical expressions (5) and (6),and

wear resistance of the tread and crack resistance in the grooves areevaluated based on determination in the determining and evaluating ofdurability.

The tire is designed and manufactured based on an evaluation result inthe determining and evaluating of durability.

Fa=((Dd+De)/W)×100   (1)

0.02626×A−1.8615<Fa   (2)

Fa<0.02626×A−0.6615   (3)

Gs=((Da−Dh)/W)×100   (4)

−0.010819×A−0.084658<Gs   (5)

Gs<−0.010819×A+0.6713   (6)

Advantageous Effects of the Invention

In the pneumatic tire according to the present invention, generation ofcracks in groove bottoms is reduced. In the tire, generation of unevenwear of a tread is reduced. In the durability evaluation methodaccording to the present invention, durability of a pneumatic tire canbe easily evaluated. In a manufacturing method for a tire according tothe present invention, a tire excellent in durability can be easilymanufactured.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a portion of a pneumatic tireaccording to one embodiment of the present invention.

FIG. 2 is an enlarged cross-sectional view of a portion of the tireshown in FIG. 1.

FIG. 3 is an enlarged cross-sectional view of another portion of thetire shown in FIG. 1.

FIG. 4 is a cross-sectional view of a portion of a pneumatic tireaccording to another embodiment of the present invention.

FIG. 5 shows a graph representing a relationship between an aspect ratioand a sum Fa of amounts of protrusions for a sidewall.

FIG. 6 shows a graph representing a relationship between an aspect ratioand a difference Gs in amount of protrusion for a tread.

DESCRIPTION OF EMBODIMENTS

The following will describe in detail the present invention based onpreferred embodiments with reference where appropriate to theaccompanying drawing.

FIG. 1 illustrates a pneumatic tire 2. In FIG. 1, the up-down directionrepresents the radial direction of the tire 2, the right-left directionrepresents the axial direction of the tire 2, and the directionperpendicular to the surface of the sheet represents the circumferentialdirection of the tire 2. An alternate long and short dash line CL inFIG. 1 represents the equator plane of the tire 2. The tire 2 has ashape which is symmetric about the equator plane except for a treadpattern. An alternate long and two short dashes line BL represents thebead base line of the tire 2.

The tire 2 includes a tread 4, sidewalls 6, beads 8, a carcass 10, abelt 12, a band 14, an inner liner 16, and chafers 18. The tire 2 is ofa tubeless type. The tire 2 is mounted to passenger cars.

The tread 4 has a shape that projects outward in the radial direction.The tread 4 has a center region C and shoulder regions S. The centerregion C is disposed at the center, in the axial direction, of the tire2. The paired shoulder regions S are disposed outward of the centerregion C in the axial direction. The tread 4 forms a tread surface 20that can contact with a road surface. The tread surface 20 has grooves22 formed therein. A tread pattern is formed by the grooves 22.

The tread 4 includes a base layer and a cap layer, which are not shown.The cap layer is disposed outward of the base layer in the radialdirection. The cap layer is layered over the base layer. The base layeris formed of a crosslinked rubber excellent in adhesiveness. A typicalbase rubber of the base layer is a natural rubber. The cap layer isformed of a crosslinked rubber excellent in wear resistance, heatresistance, and grip performance.

Each sidewall 6 extends from the edge of the tread 4 in almost radiallyinward direction. The outer ends, in the radial direction, of thesidewalls 6 are joined to the tread 4. The sidewalls 6 are formed of acrosslinked rubber excellent in cut resistance and weather resistance.The sidewalls 6 prevent the carcass 10 from being damaged.

The beads 8 are disposed inward of the sidewalls 6 in the radialdirection. Each bead 8 includes a core 24 and an apex 26 that extendsoutward of the core 24 in the radial direction. The core 24 isring-shaped, and includes a non-stretchable wound wire. A typicalmaterial of the wire is a steel. The apex 26 is tapered outward in theradial direction. The apex 26 is formed of a highly hard crosslinkedrubber.

The carcass 10 includes a carcass ply 28. The carcass ply 28 is extendedalong the tread 4 and the sidewalls 6 on and between the beads 8 on bothsides. The carcass ply 28 is turned up around each core 24 from theinner side toward the outer side in the axial direction. By the carcassply 28 being turned up, the carcass ply 28 includes a main body portion28 a and turned-up portions 28 b.

The carcass ply 28 is formed of multiple cords aligned with each other,and a topping rubber. An absolute value of an angle of each cordrelative to the equator plane ranges from 75° to 90°. In other words,the carcass 10 forms a radial structure. The cords are formed of anorganic fiber. Preferable examples of the organic fiber includepolyester fibers, nylon fibers, rayon fibers, polyethylene naphthalatefibers, and aramid fibers. The carcass 10 may be formed of two or moreplies.

The belt 12 is disposed inward of the tread 4 in the radial direction.The belt 12 is layered over the carcass 10. The belt 12 reinforces thecarcass 10. The belt 12 includes an inner layer 30, and an outer layer32 disposed outward of the inner layer 30 in the radial direction so asto be layered over the inner layer 30. As is apparent from FIG. 1, thewidth of the inner layer 30 is slightly greater than the width of theouter layer 32 in the axial direction. Each of the inner layer 30 andthe outer layer 32 is formed of multiple cords aligned with each other,and a topping rubber, which are not shown. Each cord is inclinedrelative to the equator plane. The absolute value of the inclinationangle is typically greater than or equal to 10°, and not greater than35°. A direction in which the cords of the inner layer 30 are inclinedrelative to the equator plane and a direction in which the cords of theouter layer 32 are inclined relative to the equator plane are oppositeto each other. A material of each cord is preferably a steel. For eachcord, an organic fiber may be used.

A double-headed arrow Wb in FIG. 1 represents a width of the belt 12.The width Wb of belt 12 is measured as a distance in a straight line inthe axial direction of the tire 2. The width Wb is measured as a widthof a range in which the inner layer 30 and the outer layer 32 arelayered over each other. In the tire 2, the width Wb is measured as awidth of the outer layer 32. The width Wb is preferably greater than orequal to 0.58 times the maximum width of the tire 2, and preferably notgreater than 0.85 times the maximum width of the tire 2.

The band 14 is disposed outward of the belt 12 in the radial direction.The band 14 includes a full band 34 and a pair of edge bands 36. Thewidth of the full band 34 is greater than the width of the belt 12 inthe axial direction. The full band 34 covers the belt 12. The full band34 is formed of a cord and a topping rubber, which are not shown. Thecord of the full band 34 is helically wound. The full band 34 has aso-called jointless structure. The cord of the full band 34 extendssubstantially in the circumferential direction. An angle of the cordrelative to the circumferential direction is less than or equal to 5°,and more preferably less than or equal to 2°.

The pair of edge bands 36 cover end portions, in the axial direction, ofthe belt 12. The edge bands 36 are disposed outward of the full band 36in the radial direction, and layered over end portions, in the axialdirection, of the full band 34. Each edge band 36 is formed of a cordand a topping rubber. The cord of each edge band 36 is helically wound.The full band 34 has a so-called jointless structure. The cord of thefull band 34 extends substantially in the circumferential direction. Anangle of the cord relative to the circumferential direction is less thanor equal to 5°, and more preferably less than or equal to 2°. The edgebands 36 may be disposed inward of the full band 36 in the radialdirection and layered. The cord of each edge band 36 may extendsubstantially in the axial direction.

The belt 12 is held by the band 14, thereby reducing lifting of the belt12. The cords of the band are formed of an organic fiber. Preferableexamples of the organic fiber include nylon fibers, polyester fibers,rayon fibers, polyethylene naphthalate fibers, and aramid fibers.

The belt 12 and the band 14 form a reinforcing layer. The reinforcinglayer may be formed merely by the belt 12.

The inner liner 16 is disposed inward of the carcass 10. The inner liner16 is formed of a crosslinked rubber. For the inner liner 16, a rubberexcellent in airtightness is used. A typical base rubber of the innerliner 16 is an isobutylene-isoprene-rubber or halogenatedisobutylene-isoprene-rubber. The inner liner 16 maintains internalpressure of the tire.

The chafers 18 are disposed near the beads 8. When the tire 2 is mountedto a rim, the chafers 18 contact with the rim. Regions near the beads 8are protected due to the contact. For example, the chafers 18 are formedof a fabric and a rubber impregnated into the fabric.

In FIG. 1, a point Pa represents a point of intersection between theequator plane and the tread surface 20. An alternate long and two shortdashes line Lh represents a straight line that extends in the radialdirection. A double-headed arrow Wh represents a width between onestraight line Lh on one side in the axial direction and the otherstraight line Lh, on the other side in the axial direction, which is notshown. The width Wh is 0.8 times the width Wb of the belt 12, that is,0.8·Wb. A point Ph represents a point of intersection between thestraight line Lh and the tread surface 20.

An alternate long and two short dashes line Le represents a straightline that extends in the axial direction with the maximum width of thetire 2. The maximum width represents a width, in the axial direction, ofthe tire between axially outermost positions of the main body portion 28a of the carcass 10 which is extended. A point Pe represents a point ofintersection between the straight line Le and an axially outer sidesurface 6 a of each sidewall 6. The maximum width of the tire 2 ismeasured as a distance from the point Pe to the point Pe on the otherside, which is not shown. A double-headed arrow D represents a distance,in the radial direction, from the point Pa to the point Pe. An alternatelong and two short dashes line Ld represents a straight line thatextends in the axial direction through the midpoint of the distance D. Apoint Pd represents a point of intersection between the straight line Ldand the axially outer side surface 6 a of each sidewall 6. The point Pdrepresents the midpoint, in the radial direction, between the point Paand the point Pe.

FIG. 2 is an enlarged view of a portion of the tire 2. The axially outerside surface 6 a of the tire 2 represents a state where the tire 2 ismounted to a normal rim, and is inflated with air to a normal internalpressure P. An alternate long and two short dashes line 6 a′ alsorepresents the axially outer side surface of the tire 2. The outer sidesurface 6 a′ represents a state where the tire 2 is mounted to a normalrim, and is inflated with air to an air pressure of 0.05·P which is 0.05times the normal internal pressure P.

A point Pd′ represents a point of intersection between the outer sidesurface 6 a′ and a normal line to the axially outer side surface 6 a atthe point Pd. A double-headed arrow Dd represents a distance from thepoint Pd′ to the point Pd. The distance Dd represents an amount ofprotrusion of the tire 2 at the point Pd. The amount of protrusion Ddrepresents a distance from the point Pd′ to the point Pd in a statewhere the tire is pressurized to shift from the air pressure of 0.05·Pto the air pressure P. The amount of protrusion Dd is represented so asto indicate a plus value in the case of shift in the axially outwarddirection and indicate a minus value in the case of shift in the axiallyinward direction.

A point Pe′ represents a point of intersection between the straight lineLe and the outer side surface 6 a′. A double-headed arrow De representsa distance from the point Pe′ to the point Pe. The distance Derepresents an amount of protrusion of the tire 2 at the point Pe. Theamount of protrusion De represents a distance from the point Pe′ to thepoint Pe in a state where the tire is pressurized to shift from the airpressure of 0.05·P to the air pressure P. The amount of protrusion De isrepresented so as to indicate a plus value in the case of shift in theaxially outward direction, and indicate a minus value in the case ofshift in the axially inward direction.

FIG. 3 is an enlarged view of another portion of the tire 2. The treadsurface 20 of the tire 2 represents a state where the tire 2 is mountedto a normal rim, and is inflated with air to a normal internal pressureP. An alternate long and two short dashes line 20′ also represents thetread surface of the tire 2. The tread surface 20′ represents a statewhere the tire 2 is mounted to a normal rim, and is inflated with air toan air pressure of 0.05·P which is 0.05 times the normal internalpressure P.

A point Pa′ represents a point of intersection between the equator planeand the tread surface 20′. A double-headed arrow Da represents adistance from the point Pa′ to the point Pa. The distance Da representsan amount of protrusion of the tire 2 at the point Pa. The amount ofprotrusion Da represents a distance from the point Pa′ to the point Pain a state where the tire is pressurized to shift from the air pressureof 0.05·P to the air pressure P. The amount of protrusion Da isrepresented so as to indicate a plus value in the case of shift in theradially outward direction, and indicate a minus value in the case ofshift in the radially inward direction.

A point Ph′ represents a point of intersection between the tread surface20′ and a normal line to the tread surface 20 at the point Ph. Adouble-headed arrow Dh represents a distance from the point Ph′ to thepoint Ph. The distance Dh represents an amount of protrusion of the tire2 at the point Ph. The amount of protrusion Dh represents a distancefrom the point Ph′ to the point Ph in a state where the tire ispressurized to shift from the air pressure of 0.05·P to the air pressureP. The amount of protrusion Dh is represented so as to indicate a plusvalue in the case of shift in the radially outward direction andindicate a minus value in the case of shift in the radially inwarddirection.

The tire 2 is mounted to a normal rim and is inflated with air to theair pressure of 0.05·P. A profile of the tire 2 under the air pressureof 0.05·P is measured by a profile measurement machine. Further, thetire is inflated with air to the air pressure P. A profile of the tire 2under the air pressure P is measured by the profile measurement machine.The point Pa, the point Ph, the point Pe, and the point Pd are obtainedbased on the profile of the tire 2 under the air pressure P. The profileof the tire 2 under the air pressure P and the profile of the tire 2under the air pressure of 0.05·P are overlaid on each other such thatbead positions (rim flange positions) of the profiles are aligned witheach other. The point Pa′, the point Ph′, the point Pe′, and the pointPd′ are obtained based on the profile of the tire 2 under the airpressure of 0.5·P. Thus, the amount of protrusion Da and the amount ofprotrusion Dh for the tread 4, and the amount of protrusion Dd and theamount of protrusion De for each sidewall 6 are obtained.

A sum Fa of the amounts of protrusions for each sidewall 6 is calculatedbased on a sum of the amount of protrusion Dd and the amount ofprotrusion De, and a nominal width W of the tire 2, according to thefollowing expression.

Fa=((Dd+De)/W)×100   (1)

In the tire 2, the aspect ratio is 70%. In the tire 2, the sum Fa of theamounts of protrusions satisfies the following relational expression.

−0.02<Fa<1.18

In the tire 2 having the high aspect ratio, when both the amount ofprotrusion Dd and the amount of protrusion De are increased, theshoulder region S of the tread 4 is likely to protrude in the radiallyoutward direction. By the protruding of the shoulder region S, expansionof the openings of the grooves 22 is reduced. In the tire 2, the sum Faof the amounts of protrusions is greater than −0.02. Therefore,expansion of the openings of the grooves 22 is reduced. In the tire 2,generation of cracks in the groove bottoms is reduced. In thedescription herein, the high aspect ratio represents an aspect ratiothat is higher than or equal to 65%.

On the other hand, when both the amount of protrusion Dd and the amountof protrusion De are excessively increased, the shoulder region S of thetread 4 is protruded in the radially inward direction. Contact pressureat the shoulder region S is lowered. The shoulder region S in which thecontact pressure is low, is likely to slide and the tread surface 20 islikely to be worn. In the tire 2, the sum Fa of the amounts ofprotrusions is less than 1.18. Therefore, the shoulder region S is lesslikely to be greatly protruded. In the tire 2, uneven wear of theshoulder region S is reduced.

A difference Gs in the amount of protrusion for the tread 4 iscalculated based on a difference between the amount of protrusion Da andthe amount of protrusion Dh, and the nominal width W of the tire 2,according to following expression.

Gs=((Da−Dh)/W)×100   (4)

In the tire 2, the difference Gs in the amount of protrusion satisfiesthe following relational expression.

−0.84<Gs<−0.09

When the amount of protrusion Da is reduced and the amount of protrusionDh is increased, openings of the grooves 22 are likely to be expanded.Openings of the grooves 22 that extend in the circumferential directionare likely to be expanded. In particular, openings of the grooves 22disposed in the shoulder region S are likely to be expanded. When theopenings of the grooves 22 are expanded, tensile stress is applied, inthe groove width direction, to the bottom portions of the grooves 22that extend in the circumferential direction. Due to the tensile stress,cracks are likely to be generated in the bottom portions of the grooves22. Further, contact pressure of the tread surface 20 in the shoulderregion S is enhanced. Uneven wear of the tread surface 20 in theshoulder region S is increased.

In the tire 2, the difference Gs in the amount of protrusion is greaterthan −0.84. The amount of protrusion Dh is less likely to be excessivelyincreased with respect to the amount of protrusion Da. In the tire 2,generation of cracks in the bottom portions of the grooves 22 isreduced. Uneven wear of the tread surface 20 in the shoulder region S isreduced.

On the other hand, when the amount of protrusion Da is increased and theamount of protrusion Dh is reduced, the center region C of the tread 4protrudes in the radially outward direction. In the center region C,contact pressure at the tread 4 is enhanced. When the tire 2 is mountedto a drive wheel, wear is likely to increase at the tread surface 20 inthe center region C in which contact pressure is high. When the tire 2is mounted to a driven wheel (idler wheel), the tread surface 20 in theshoulder region S in which contact pressure is low, is likely to slide.Thus, wear of the tread surface 20 in the shoulder region S is likely toincrease.

In the tire 2, the difference Gs in the amount of protrusion is lessthan −0.09 (−0.086). The amount of protrusion Da is less likely to beexcessively increased with respect to the amount of protrusion Dh. Inthe tire 2, the center region C is less likely to protrude. In the tire2, uneven wear of the tread surface 20 is reduced.

For the tire 2, the sum Fa of the amounts of protrusions and thedifference Gs in the amount of protrusion are each represented as aratio with respect to the nominal width W of the tire 2. Thus, thedifference Fa in the amount of protrusion and the difference Gs in theamount of protrusion are applicable to tires having different nominalwidths W.

In the tire 2 having the edge bands 36, protrusion of the shoulderregions S of the tread surface 20 is reduced. In the tire 2, when thetire 2 is inflated with air to a normal internal pressure, protrusion ofthe shoulder region S is small. In particular, in the tire 2 having ahigh aspect ratio in which the aspect ratio A is higher than or equal to65%, the shoulder region S is likely to be protruded. In the tire 2 ofthis kind, an effect of reducing protrusion by the edge bands 36 isgreat.

In the present invention, the dimensions and angles of the components ofthe tire 2 are measured in a state where the tire 2 is mounted to anormal rim, and inflated with air to a normal internal pressure, unlessotherwise specified. During the measurement, no load is applied to thetire 2. In the description herein, the normal rim represents a rim thatis specified according to the standard with which the tire 2 complies.The “standard rim” in the JATMA standard, the “Design Rim” in the TRAstandard, and the “Measuring Rim” in the ETRTO standard are included inthe normal rim. In the description herein, the normal internal pressurerepresents an internal pressure that is specified according to thestandard with which the tire complies. The “maximum air pressure” in theJATMA standard, the “maximum value” recited in “TIRE LOAD LIMITS ATVARIOUS COLD INFLATION PRESSURES” in the TRA standard, and the“INFLATION PRESSURE” in the ETRTO standard, are included in the normalinternal pressure.

FIG. 4 illustrates another pneumatic tire 42 according to the presentinvention. In the description herein, components thereof different fromthose of the tire 2 will be mainly described. Description of the samecomponents as for the tire 2 is not given. The tire 42 includes a tread44, sidewalls 46, beads 48, a carcass 50, a belt 52, a band 54, an innerliner 56, and chafers 58.

The tread 44 forms a tread surface 60 that can contact with a roadsurface. The tread surface 60 has grooves 62 formed therein. Each bead48 includes a core 64 and an apex 66 that extends outward of the core 64in the radial direction.

The carcass 50 includes a first ply 68 and a second ply 70. The firstply 68 and the second ply 70 are extended along the tread 44 and thesidewalls 46 on and between the beads on both sides. The first ply 68 isturned up around each core 64 from the inner side toward the outer sidein the axial direction. By the first ply 68 being turned up, the firstply 68 includes a main body portion 68 a and turned-up portions 68 b.The second ply 70 is turned up around each core 64 from the inner sidetoward the outer side in the axial direction. By the second ply 70 beingturned up, the second ply 70 includes a main body portion 70 a andturned-up portions 70 b. The ends of the turned-up portions 68 b of thefirst ply 68 are disposed radially outward of the ends of the turned-upportions 70 b of the second ply 70.

Each of the first ply 68 and the second ply 70 is formed of multiplecords aligned with each other, and a topping rubber. An absolute valueof an angle of each cord relative to the equator plane ranges from 75°to 90°. In other words, the carcass forms a radial structure. The cordsare formed of an organic fiber. Preferable examples of the organic fiberinclude polyester fibers, nylon fibers, rayon fibers, polyethylenenaphthalate fibers, and aramid fibers. The carcass 50 may be formed ofone ply.

The belt 52 is disposed inward of the tread 44 in the radial direction.The belt 52 is layered over the carcass 50. The belt 52 includes aninner layer 72 and an outer layer 74. Each of the inner layer 72 and theouter layer 74 is formed of multiple cords aligned with each other, anda topping rubber, which are not shown. Each cord is inclined relative tothe equator plane. The absolute value of the inclination angle istypically greater than or equal to 10° and not greater than 35°. Adirection in which the cords of the inner layer 72 are inclined relativeto the equator plane is opposite to a direction in which the cords ofthe outer layer 74 are inclined relative to the equator plane.

The band 54 is disposed outward of the belt 52 in the radial direction.The band 54 includes a full band 76 and a pair of edge bands 78. Thewidth of the full band 76 is greater than the width of the belt 52 inthe axial direction. The full band 76 and the edge bands 78 are eachformed of a cord and a topping rubber, which are not shown. The cordsare helically wound. The full band 76 and the edge bands 78 each have aso-called jointless structure. The cords of the full band 76 and theedge bands 78 extend substantially in the circumferential direction. Thecords of the edge bands 78 may extend substantially in the axialdirection. The edge bands 78 may be disposed inward of the full band 76in the radial direction and layered. The belt 52 and the band 54 form areinforcing layer.

In the tire 42, an aspect ratio is 40%. In the tire 42, a sum Fa ofamounts of protrusions satisfies the following relational expression.

−0.81<Fa<0.39

In the tire 42 having the low aspect ratio, even when both the amount ofprotrusion Dd and the amount of protrusion De are increased, protrusionof the shoulder region S of the tread 44 in the radially outwarddirection is small. An effect of reducing expansion of the openings ofthe grooves 62 is low. When both the amount of protrusion Dd and theamount of protrusion De are increased, the shoulder region S of thetread 44 is drawn in the axially outward direction. Thus, in the tire42, openings of the grooves 62 that extend in the circumferentialdirection are expanded. In the description herein, the low aspect ratiorepresents an aspect ratio that is less than or equal to 50%.

In the tire 42, the sum Fa of the amounts of protrusions is less than0.39. Therefore, expansion of the openings of the grooves 62 that extendin the circumferential direction is reduced. In the tire 2, generationof cracks in the groove bottoms is reduced.

In the tire 42, the span of each sidewall 46 in the radial direction isshort. Since the span in the radial direction is short, when both theamount of protrusion Dd and the amount of protrusion De are reduced, theshoulder region S of the tread 44 is likely to protrude in the radiallyoutward direction. In the shoulder region S, contact pressure at thetread 44 is enhanced. In the shoulder region S, the tread surface 60 islikely to be worn.

In the tire 42, the sum Fa of the amounts of protrusions is greater than−0.81. Therefore, the shoulder region S is less likely to be greatlyprotruded. In the tire 42, uneven wear of the shoulder region S isreduced.

In the tire 42, the difference Gs in the amount of protrusion satisfiesthe following relational expression.

−0.52<Gs<0.24

In the tire 42, the difference Gs in the amount of protrusion is greaterthan −0.52. Thus, the amount of protrusion Dh is less likely to beexcessively increased with respect to the amount of protrusion Da. Inthe tire 42, generation of cracks in the bottom portions of the grooves62 is reduced. Further, uneven wear of the tread surface 60 in theshoulder region S is reduced.

On the other hand, in the tire 42, the difference Gs in the amount ofprotrusion is less than 0.24. Therefore, the amount of protrusion Da isless likely to be excessively increased with respect to the amount ofprotrusion Dh. In the tire 42, the center region C is less likely toprotrude. In the tire 42, uneven wear of the tread surface 60 isreduced.

Preferable ranges for the sum Fa of the amounts of protrusions and thedifference Gs in the amount of protrusion are each different accordingto the aspect ratio A as described for the tire 2 and the tire 42 asexamples.

FIG. 5 shows a graph representing a distribution, of sample tires, basedon the aspect ratio A and the sum Fa of the amounts of protrusions. Inthe graph, circle marks represent a distribution of the sample tires inwhich generation of cracks and generation of uneven wear of the shoulderregion S were favorably reduced. In the graph, X marks represent adistribution of the sample tires in which at least one of cracks anduneven wear of the shoulder region S was unfavorably generated.According to the graph, it has been confirmed that, in the sample tiresin which the value Fa is less than values on a straight line Lv andgreater than values on a straight line Lw, generation of cracks in thegroove bottoms and generation of uneven wear are particularly favorablyreduced.

The straight line Lv may be represented by the following expression.

Fa=0.02626×A−0.6615

On the other hand, the straight line Lw may be represented by thefollowing expression.

Fa=0.02626×A−1.8615

In a case where the sum Fa of the amounts of protrusions satisfies thefollowing relational expressions in which A represents an aspect ratio,generation of cracks in the groove bottoms can be reduced and unevenwear of the tread can be reduced.

0.02626×A−1.8615<Fa   (2)

Fa<0.02626×A−0.6615   (3)

FIG. 6 shows a graph representing a distribution, of sample tires, basedon the aspect ratio A and the difference Gs in the amount of protrusion.In the graph, circle marks represent a distribution of the sample tiresin which generation of cracks and generation of uneven wear of theshoulder region S were favorably reduced. In the graph, X marksrepresent a distribution of the sample tires in which at least one ofcracks and uneven wear of the shoulder region S was unfavorablygenerated. According to the graph, it has been confirmed that, in thesample tires in which the difference Gs in the amount of protrusionrepresents a value that is less than values on a straight line Lt andgreater than values on a straight line Lu, generation of cracks in thegroove bottoms and generation of uneven wear are particularly favorablyreduced.

The straight line Lt may be represented by the following expression.

Gs=−0.010819×A+0.6713

On the other hand, the straight line Lu may be represented by thefollowing expression.

Gs=−0.010819×A−0.084658

In a case where the difference Gs in the amount of protrusion satisfiesthe following relational expressions in which A represents an aspectratio, generation of cracks in the groove bottoms can be reduced anduneven wear of the tread can be reduced.

−0.010819×A−0.084658<Gs   (5)

Gs<−0.010819×A+0.6713   (6)

In the tire 2 according to the present invention, when the sum Fa of theamounts of protrusions satisfies the above mathematical expressions (2)and (3), generation of cracks in the groove bottoms and uneven wear ofthe tread 4 can be reduced. Further, when the difference Gs in theamount of protrusion for the tread 4 satisfies the above mathematicalexpressions (5) and (6), generation of cracks in the groove bottoms anduneven wear of the tread can be reduced.

Further, also in the tire 42, when the sum Fa of the amounts ofprotrusions satisfies the above mathematical expressions (2) and (3),and the difference Gs in the amount of protrusion for the tread 44satisfies the above mathematical expressions (5) and (6), the sameeffects as for the tire 2 can be obtained.

Next, a manufacturing method according to the present invention will bedescribed for the tire 2 as an example. The manufacturing methodincludes a determination step of evaluating durability of a sample tire.In the determination step, a sample tire for obtaining the tire 2 isprepared. Whether or not the sample tire is good is determined based onthe sum Fa of the amounts of protrusions and the difference Gs in theamount of protrusion. Based on evaluation results in the determinationstep, the tire 2 is designed. For example, when the sample tire isdetermined as being not good, a carcass line is adjusted such that eachof the sum Fa of the amounts of protrusions and the difference Gs in theamount of protrusion is within a predetermined range.

The carcass line is adjusted by adjusting, for example, a shape of amold for vulcanization and molding. In the adjustment of the carcassline, for example, a radius of curvature of the carcass line near thepoint Pd and a radius of curvature of the carcass line near the point Peare adjusted by the shape of the mold. Thus, a sample tire in which thesum Fa of the amounts of protrusions and the difference Gs in the amountof protrusion are good, can be obtained. The tire 2 is manufacturedaccording to the mold for forming the sample tire. In this manner, thetire 2 is designed and manufactured according to the sample tire,thereby facilitating manufacturing of the tire 2 excellent indurability.

In the description herein, as a method for adjusting each of the sum Faof the amounts of protrusions and the difference Gs in the amount ofprotrusion so as to be within the predetermined range, a method foradjusting the carcass line is described as an exemplary method. However,the adjustment method is not limited to the above-described exemplarymethod. For example, the adjustment can be made by adjusting a thicknessof rubber of the sidewall 6 near the point Pd and a thickness of rubberof the sidewall 6 near the point Pe. Further, as a method for adjustingeach of the sum Fa of the amounts of protrusions and the difference Gsin the amount of protrusion so as to be within the predetermined range,the structure of the band 14 of the tire 2 may be changed.

Further, an exemplary evaluation method according to the presentinvention will be described for the tire 2 as an example. The evaluationmethod includes a step of obtaining a tire assembly, a low internalpressure step, a normal internal pressure step, and a determinationstep.

In the step of obtaining a tire assembly, the tire 2 is mounted to anormal rim, to obtain a tire assembly.

In the low internal pressure step, the tire assembly is inflated withair to an air pressure of 0.05·P, as an internal pressure, which is 0.05times the normal internal pressure P. In a state where the tire assemblyhas been inflated with air to the air pressure of 0.05·P, a profile ofthe tire 2 is obtained.

In the normal internal pressure step, after the low internal pressurestep, the tire assembly is inflated with air to the normal internalpressure. In a state where the tire assembly has been inflated with airto the normal internal pressure P, a profile of the tire 2 is obtained.

In the determination step, positions of the point Pa, the point Ph, thepoint Pd, and the point Pe are obtained based on the profile obtained inthe normal internal pressure step. Further, positions of the point Pa′,the point Ph′, the point Pd′, and the point Pe′ are obtained based onthe profile obtained in the low internal pressure step. The amounts ofprotrusions Da and Dh for the tread 4 and the amounts of protrusions Deand Dd for each sidewall 6 are calculated. Next, the difference Gs inthe amount of protrusion for the tread 4 and the sum Fa of the amountsof protrusions for each sidewall 6 are calculated. Whether or not eachof the sum Fa of the amounts of protrusions and the difference Gs in theamount of protrusion is within a predetermined range is determined forevaluation. When the sum Fa and the difference Gs are each within thepredetermined range, the evaluation result is determined as being good.When each of the sum Fa and the difference Gs is not within thepredetermined range, the evaluation result is determined as being notgood.

In the evaluation method, durability of the tire 2 can be efficientlydetermined in terms of generation of cracks in the bottom portions ofthe grooves 22, and generation of uneven wear of the tread 4.

EXAMPLES

Hereinafter, effects of the present invention will become apparentaccording to examples. However, the present invention should not berestrictively construed based on the description of examples.

Band structures of examples and comparative examples described below areindicated in tables with the use of reference characters. The referencecharacters represent the following structures.

-   “1F+1F′”: structure where two full bands are used, that is, one full    band that has a cord extending in the circumferential direction, and    one full band that has a cord extending in the axial direction, are    used.-   “1F”: structure where one full band is used, that is, one full band    that has a cord extending in the circumferential direction, is used.-   “1E+1F”: structure where a pair of edge bands each of which has a    cord extending in the circumferential direction, and one full band    that has a cord extending in the circumferential direction, are    used.

Example 1

A tire having the fundamental structure shown in FIG. 1 was produced asa sample of a tire. The size of the tire was “185/70R14”. That is, thenominal width W of the tire was 185 (mm), and the aspect ratio A thereofwas 70%. The tire was mounted to a normal rim of 14×5.5 J. The tire wasinflated with air to an internal pressure of 12 kPa. Thereafter, thetire was inflated with air to the normal internal pressure of 240 kPa.The amount of protrusion Da (mm), the amount of protrusion Dh (mm), theamount of protrusion Dd (mm), the amount of protrusion De (mm), thedifference Gs in the amount of protrusion, and the sum Fa of the amountsof protrusions, were obtained. The results are indicated in Table 1.

Example 2 to 3 and Comparative Example 1 to 2

Tires were produced as samples of tires in the same manner as forexample 1 except that the carcass lines were adjusted. For the tires,the amounts of protrusions (Da (mm), Dh (mm), Dd (mm), and De (mm)), thedifference Gs in the amount of protrusion, and the sum Fa of the amountsof protrusions, were obtained. The results are indicated in Table 1.

Example 4 to 7 and Comparative Example 3 to 4

Tires were produced as samples of tires in the same manner as forexample 1 except that the band structures were different and the carcasslines were adjusted. For the tires, the amounts of protrusions (Da (mm),Dh (mm), Dd (mm), and De (mm)), the difference Gs in the amount ofprotrusion, and the sum Fa of the amounts of protrusions, were obtained.The results are indicated in Table 2.

Example 8

A tire having the fundamental structure shown in FIG. 4 was produced asa sample of a tire. The size of the tire was “225/40R18”. That is, thenominal width W of the tire was 225 (mm), and the aspect ratio A thereofwas 40%. The tire was mounted to a normal rim of 18×8 J. The tire wasinflated with air to an internal pressure of 12 kPa. Thereafter, thetire was inflated with air to the normal internal pressure of 240 kPa.The amount of protrusion Da (mm) and the amount of protrusion Dh (mm)for a tread, and the amount of protrusion Dd (mm) and the amount ofprotrusion De (mm) for a sidewall, were obtained. The difference Gs inthe amount of protrusion and the sum Fa of the amounts of protrusions,were obtained. The results are indicated in Table 3.

Example 9 to 10 and Comparative Example 5 to 6

Tires were produced as samples of tires in the same manner as forexample 8 except that the carcass lines were adjusted. For the tires,the amounts of protrusions (Da (mm), Dh (mm), Dd (mm), and De (mm)), thedifference Gs in the amount of protrusion, and the sum Fa of the amountsof protrusions, were obtained. The results are indicated in Table 3.

Example 11 to 14 and Comparative Example 7 to 8

Tires were produced as samples of tires in the same manner as forexample 8 except that the band structures were different and the carcasslines were adjusted. For the tires, the amounts of protrusions (Da (mm),Dh (mm), Dd (mm), and De (mm)), the difference Gs in the amount ofprotrusion, and the sum Fa of the amounts of protrusions, were obtained.The results are indicated in Table 4.

[Evaluation for Expansion of Cut Opening]

The tires produced as the samples of tires were mounted to the normalrims, to obtain tire assemblies. Each tire assembly was inflated withair to the normal internal pressure. Bottoms of the main grooves formedin the shoulder region in the circumferential direction in each tirewere cut in the circumferential direction. A razor blade having athickness of 0.25 mm was used to cut the bottoms of the main grooves bya depth of 2 mm and a length of 8 mm. Shapes of the cut openings weretaken and an amount of expansion of the cut opening was measured. Themeasurement results are indicated as indexes in Tables 1 to 4. The lessthe amount of expansion of the cut opening is, the greater the index is.The greater the index is, the less generation of cracks is.

[Evaluation for Wear of Shoulder Region]

The tires produced as the samples of tires were mounted to the normalrims, to obtain tire assemblies. Each tire assembly was inflated withair to the normal internal pressure. Each tire assembly was mounted to abench measurement device for measuring wear energy. The tire assemblywas set so as to be rotatable. A slip angle was set as 1°. The tire wasunder a load that was 80% of the maximum load in the load indexstandard. The tire was settled on a setting table of the benchmeasurement device for measuring wear energy. Thus, wear energy of eachtire in a turning state was measured.

In the measurement of wear energy, a wear energy Es in the shoulderregion on the outer side in the turning radius direction and a wearenergy Ec at the center region were measured. A wear energy ratio(Es/Ec) of the wear energy Es to the wear energy Ec was obtained. As thewear energy ratio (Es/Ec) is increased, the shoulder region is morelikely to be worn as compared to the center region, and uneven wear ismore likely to increase. The wear energy ratio (Es/Ec) is indicated asan index and the results are indicated in Tables 1 to 6. The less thewear energy ratio (Es/Ec) is, the greater the index is. The greater theindex is, the less generation of uneven wear of the shoulder region is.

TABLE 1 Evaluation results Comparative Exam- Exam- Exam- Comparativeexample 1 ple 2 ple 1 ple 3 example 2 Da (mm) 0.12 0.24 0.54 0.66 0.90Dh (mm) 1.70 1.56 1.8 1.14 1.02 Dd (mm) 0.15 0.15 0.35 1.15 1.15 De (mm)0.90 0.90 0.50 0.20 0.20 Gs −0.85 −0.71 −0.68 −0.26 −0.06 Fa 0.57 0.570.46 0.73 0.73 Band structure 1E + 1F 1E + 1F 1E + 1F 1E + 1F 1E + 1FExpansion of 6.6 7.3 7.5 8.1 8.8 cut in groove Wear at 7.6 8.1 9.2 7.46.8 shoulder region

TABLE 2 Evaluation results Comparative Comparative example 3 Example 6Example 4 Example 5 Example 7 example 4 Da (mm) 0.78 0.78 0.48 0.18 0.060 Dh (mm) 1.74 1.92 1.56 1.32 1.02 0.84 Dd (mm) −0.10 0.0 0.3 0.10 0.951.20 De (mm) −1.0 0.0 0.4 0.80 0.95 1.20 Gs −0.52 −0.62 −0.58 −0.62−0.52 −0.45 Fa −0.11 0.0 0.38 0.49 1.03 1.03 Band 1F 1F 1F + 1F′ 1F +1F′ 1F + 1F′ 1F + 1F′ structure Expansion 6.9 7.6 8.1 8.0 8.1 8.2 of cutin groove Wear at 7.2 8 9.3 8.6 7.9 7.5 shoulder region

TABLE 3 Evaluation results Comparative Exam- Exam- Exam- Comparativeexample 5 ple 9 ple 8 ple 10 example 6 Da (mm) 0.62 0.74 1.04 1.16 1.28Dh (mm) 1.88 1.65 1.87 0.86 0.63 Dd (mm) −1.81 −0.81 −0.56 0.46 0.46 De(mm) 0.17 0.17 −0.37 −0.68 −0.68 Gs −0.56 −0.41 −0.37 0.13 0.29 Fa −0.29−0.29 −0.41 −0.10 −0.10 Band structure 1E + 1F 1E + 1F 1E + 1F 1E + 1F1E + 1F Expansion of 6.6 7.3 7.5 8.1 8.8 cut in groove Wear at 7.6 8.19.2 7.4 6.8 shoulder region

TABLE 4 Evaluation results Comparative Example Example Example ExampleComparative example 7 13 11 12 14 example 8 Da (mm) 1.28 1.28 0.98 0.680.56 0.50 Dh (mm) 1.67 1.93 1.55 1.33 0.95 0.72 Dd (mm) −1.10 −0.91−0.74 −0.97 0.27 0.62 De (mm) −1.09 −0.90 −0.61 −0.10 0.28 0.63 Gs −0.17−0.29 −0.25 −0.29 −0.17 −0.10 Fa −0.97 −0.81 −0.60 −0.47 0.25 0.56 Band1F 1F 1F + 1F′ 1F + 1F′ 1F + 1F′ 1F + 1F′ structure Expansion 6.9 7.68.0 8.0 8.1 8.2 of cut in groove Wear at 7.2 8.0 9.3 8.6 7.9 7.5shoulder region

When the amount of protrusion Dh is excessively reduced with respect tothe amount of protrusion Da, uneven wear of a tread surface may increase(see comparative example 2 and comparative example 6). On the otherhand, when the amount of protrusion Da is excessively reduced, and theamount of protrusion Dh is excessively increased, expansion of groovesin the shoulder region may increase. The tire is poor in crackresistance in the grooves (see comparative example 1 and comparativeexample 5). When, in a pneumatic tire, the sum Fa of the amounts ofprotrusions satisfies the above mathematical expressions (2) and (3),and the difference Gs in the amount of protrusion satisfies the abovemathematical expressions (5) and (6), the pneumatic tire can beexcellent in resistance to uneven wear and crack resistance in grooves(see examples 1 to 14).

As indicated in Tables 1 to 4, evaluations are higher in the tiresaccording to examples than in the tires according to comparativeexamples. The evaluation results clearly indicate that the presentinvention is superior.

INDUSTRIAL APPLICABILITY

The tire and the method for testing durability of the tire as describedabove are also applicable to various pneumatic tires for use inpassenger cars, lightweight trucks, small trucks, trucks, buses,two-wheeled automotive vehicles, and to durability tests for thepneumatic tires.

DESCRIPTION OF THE REFERENCE CHARACTERS

-   2, 42 . . . tire-   4, 44 . . . tread-   6, 46 . . . sidewall-   8, 48 . . . bead-   10, 50 . . . carcass-   12, 52 . . . belt-   14, 54 . . . band-   16, 56 . . . inner liner-   18, 58 . . . chafer-   20, 60 . . . tread surface-   22, 62 . . . groove-   24, 64 . . . core-   26, 66 . . . apex-   28 . . . carcass ply-   30, 72 . . . inner layer-   32, 74 . . . outer layer-   34, 76 . . . full band-   36, 78 . . . edge band-   68 . . . first ply-   70 . . . second ply

1. A pneumatic tire comprising: a tread having an outer surface thatforms a tread surface; a pair of sidewalls that extend almost inwardfrom ends, respectively, of the tread in a radial direction; a pair ofbeads that are disposed inward of the sidewalls in the radial direction;a carcass that is extended along inner sides of the tread and thesidewalls; and a belt that is disposed outward of the carcass in theradial direction and layered over the carcass, wherein the belt has aninner layer, and an outer layer disposed outward of the inner layer inthe radial direction and layered over the inner layer, the tread surfacehas grooves formed so as to extend in a circumferential direction, thecarcass has a carcass ply, and the carcass ply forms a main body portionthat is extended on and between one of the beads and the other of thebeads, a position, on an equator plane, of the tread surface isrepresented as a point Pa, positions, on the tread surface, which aredistant from each other by 0.8 times a width Wb, in an axial direction,of a region where the inner layer and the outer layer of the belt arelayered over each other, are each represented as a point Ph, positions,on axially outer side surfaces of the sidewalls, which are distant fromeach other with a maximum width, are each represented as a point Pe,positions, on the axially outer side surfaces of the sidewalls, each ofwhich is a midpoint between the point Pa and the point Pe in the radialdirection, are each represented as a point Pd, a nominal width isrepresented as W (mm), the maximum width is a width, in the axialdirection, between radial positions at which the main body portion ofthe carcass ply is at axially outermost positions, in an internalpressure state where an internal pressure that is 0.05 times a normalinternal pressure P has been increased to the normal internal pressureP, an amount of protrusion at the point Pa is represented as an amountof protrusion Da (mm), an amount of protrusion at the point Ph isrepresented as an amount of protrusion Dh (mm), an amount of protrusionat the point Pd is represented as an amount of protrusion Dd (mm), andan amount of protrusion at the point Pe is represented as an amount ofprotrusion De (mm), when a sum Fa of the amounts of protrusions for eachsidewall is obtained according to mathematical expression (1), the sumFa of the amounts of protrusions satisfies mathematical expressions (2)and (3) in which an aspect ratio A is used, and when a difference Gs inthe amount of protrusion for the tread is obtained according tomathematical expression (4), the difference Gs in the amount ofprotrusion satisfies mathematical expressions (5) and (6);Fa=((Dd+De)/W)×100   (1)0.02626×A−1.8615<Fa   (2)Fa<0.02626×A−0.6615   (3)Gs=((Da−Dh)/W)×100   (4)−0.010819×A−0.084658<Gs   (5)Gs<−0.010819×A+0.6713   (6).
 2. The tire according to claim 1,comprising a band disposed outward of the belt in the radial directionand layered over the belt, wherein the band includes a full band, and apair of edge bands layered over end portions, in the axial direction, ofthe full band, the full band includes a cord and a topping rubber, andthe cord extends substantially in the circumferential direction, andeach edge band includes a cord and a topping rubber, and the cordextends substantially in the circumferential direction or the axialdirection.
 3. The tire according to claim 1, wherein the aspect ratio Ais 70%, the sum Fa of the amounts of protrusions is greater than −0.02and less than 1.18, and the difference Gs in the amount of protrusion isgreater than −0.84 and less than −0.09.
 4. The tire according to claim1, wherein the aspect ratio A is 40%, the sum Fa of the amounts ofprotrusions is greater than −0.81 and less than 0.39, and the differenceGs in the amount of protrusion is greater than −0.52 and less than 0.24.5. A durability evaluation method for a tire which comprises: a treadhaving an outer surface that forms a tread surface; a pair of sidewallsthat extend almost inward from ends, respectively, of the tread in aradial direction; a pair of beads that are disposed inward of thesidewalls in the radial direction; a carcass that is extended alonginner sides of the tread and the sidewalls; and a belt that is disposedoutward of the carcass in the radial direction and layered over thecarcass, and in which: the belt has an inner layer, and an outer layerdisposed outward of the inner layer in the radial direction and layeredover the inner layer; the tread surface has grooves formed so as toextend in a circumferential direction; the carcass has a carcass ply;and the carcass ply forms a main body portion that is extended on andbetween one of the beads and the other of the beads, wherein a position,on an equator plane, of the tread surface is represented as a point Pa,positions, on the tread surface, which are distant from each other by0.8 times a width Wb, in an axial direction, of a region where the innerlayer and the outer layer of the belt are layered over each other, areeach represented as a point Ph, positions, on axially outer sidesurfaces of the sidewalls, which are distant from each other with amaximum width, are each represented as a point Pe, positions, on theaxially outer side surfaces of the sidewalls, each of which is amidpoint between the point Pa and the point Pe in the radial direction,are each represented as a point Pd, a nominal width is represented as W(mm), and the maximum width is a width, in the axial direction, betweenradial positions at which the main body portion of the carcass ply is ataxially outermost positions, and in a case where, in an internalpressure state where an internal pressure that is 0.05 times a normalinternal pressure P has been increased to the normal internal pressureP, an amount of protrusion at the point Pa is represented as an amountof protrusion Da (mm), an amount of protrusion at the point Ph isrepresented as an amount of protrusion Dh (mm), an amount of protrusionat the point Pd is represented as an amount of protrusion Dd (mm), andan amount of protrusion at the point Pe is represented as an amount ofprotrusion De (mm), wear resistance of the tread and crack resistance inthe grooves are determined as being good, when a sum Fa of the amountsof protrusions for each sidewall is obtained according to mathematicalexpression (1), the sum Fa of the amounts of protrusions satisfiesmathematical expressions (2) and (3) in which an aspect ratio A is used,and when a difference Gs in the amount of protrusion for the tread isobtained according to mathematical expression (4), the difference Gs inthe amount of protrusion satisfies mathematical expressions (5) and (6);Fa=((Dd+De)/W)×100   (1)0.02626×A−1.8615<Fa   (2)Fa<0.02626×A−0.6615   (3)Gs=((Da−Dh)/W)×100   (4)−0.010819×A−0.084658<Gs   (5)Gs<−0.010819×A+0.6713   (6).
 6. A manufacturing method for a tire whichcomprises: a tread having an outer surface that forms a tread surface; apair of sidewalls that extend almost inward from ends, respectively, ofthe tread in a radial direction; a pair of beads that are disposedinward of the sidewalls in the radial direction; a carcass that isextended along inner sides of the tread and the sidewalls; and a beltthat is disposed outward of the carcass in the radial direction andlayered over the carcass, and in which: the belt has an inner layer, andan outer layer disposed outward of the inner layer in the radialdirection and layered over the inner layer; the tread surface hasgrooves formed so as to extend in a circumferential direction; thecarcass has a carcass ply; and the carcass ply forms a main body portionthat is extended on and between one of the beads and the other of thebeads, the manufacturing method for the tire comprising the step of:determining and evaluating durability of a sample tire, wherein in thedetermining and evaluating of durability, a position, on an equatorplane, of the tread surface is represented as a point Pa, positions, onthe tread surface, which are distant from each other by 0.8 times awidth Wb, in an axial direction, of a region where the inner layer andthe outer layer of the belt are layered over each other, are eachrepresented as a point Ph, positions, on axially outer side surfaces ofthe sidewalls, which are distant from each other with a maximum width,are each represented as a point Pe, positions, on the axially outer sidesurfaces of the sidewalls, each of which is a midpoint between the pointPa and the point Pe in the radial direction, are each represented as apoint Pd, a nominal width is represented as W (mm), the maximum width isa width, in the axial direction, between radial positions at which themain body portion of the carcass ply is at axially outermost positions,and in a case where, in an internal pressure state where an internalpressure that is 0.05 times a normal internal pressure P has beenincreased to the normal internal pressure P, an amount of protrusion atthe point Pa is represented as an amount of protrusion Da (mm), anamount of protrusion at the point Ph is represented as an amount ofprotrusion Dh (mm), an amount of protrusion at the point Pd isrepresented as an amount of protrusion Dd (mm), and an amount ofprotrusion at the point Pe is represented as an amount of protrusion De(mm), it is determined that when a sum Fa of the amounts of protrusionsfor each sidewall is obtained according to mathematical expression (1),the sum Fa of the amounts of protrusions satisfies mathematicalexpressions (2) and (3) in which an aspect ratio A is used, and when adifference Gs in the amount of protrusion for the tread is obtainedaccording to mathematical expression (4), the difference Gs in theamount of protrusion satisfies mathematical expressions (5) and (6), andwear resistance of the tread and crack resistance in the grooves areevaluated based on determination in the determining and evaluating ofdurability, and the tire is designed and manufactured based on anevaluation result in the determining and evaluating of durability;Fa=((Dd+De)/W)×100   (1)0.02626×A−1.8615<Fa   (2)Fa<0.02626×A−0.6615   (3)Gs=((Da−Dh)/W)×100   (4)−0.010819×A−0.084658<Gs   (5)Gs<−0.010819×A+0.6713   (6).